At the tissue site where partial pressure of `CO_(2)` is (a)____ due to (b)____, `CO_(2)` diffuse into blood and form (c)_____ and (d)__

Answer

To solve the question step by step, we need to fill in the blanks based on the physiological processes occurring at the tissue level regarding carbon dioxide (CO2) transport.

### Step-by-Step Solution:

1. **Understanding the Context**:
- At the tissue level, cells are constantly undergoing metabolic processes, which produce CO2 as a byproduct.

2. **Identifying the Partial Pressure of CO2**:
- At the tissue site, the concentration of CO2 is high due to the continuous metabolic activities (catabolism) occurring in the cells. Therefore, the partial pressure of CO2 (A) is **high**.

3. **Reason for High CO2 Levels**:
- The high concentration of CO2 at the tissues is primarily due to **catabolism**. This is the process where organic molecules are broken down to release energy, resulting in the production of CO2. Thus, for blank (B), we write **catabolism**.

4. **Diffusion of CO2 into Blood**:
- CO2 diffuses from the tissues into the blood due to the concentration gradient, moving from an area of high concentration (tissues) to an area of lower concentration (blood).

5. **Formation of Bicarbonate**:
- Once in the blood, a significant portion of CO2 (about 70%) is converted into bicarbonate ions (HCO3-) for transport. Therefore, for blank (C), we write **bicarbonate ion**.

6. **Formation of Hydrogen Ions**:
- Along with bicarbonate ions, CO2 also leads to the formation of hydrogen ions (H+) in the blood. This occurs as CO2 reacts with water to form carbonic acid, which dissociates into bicarbonate and hydrogen ions. Hence, for blank (D), we write **H+**.

### Final Answer:
At the tissue site where partial pressure of CO2 is **high** (a) due to **catabolism** (b), CO2 diffuses into blood and forms **bicarbonate ion** (c) and **H+** (d).

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